Method for producing a graphite article

ABSTRACT

Graphite articles are produced by mixing a carbonaceous filler material and a binder of pitch with 5 to 50 percent by weight of the pitch of a chlorinated biphenyl or a chlorinated terphenyl, forming the raw batch composition thus obtained into an article, baking the article to carbonize the binder, and firing the thus baked article to graphitize it.

United States Patent Trasket al.

[451 Apr. 25, 1972 [73) Assignee:

[54] METHOD FOR PRODUCING A GRAPHITE ARTICLE [72] Inventors: Robert B. Trash, Model City, N.J.; Mark J. Smith, Wilson, N.Y.

Airco, Inc. New York, NY.

[22] Filed: May 19, 1970 [2l] Appl. No.: $7,480

Related u.s. Application um .[63] Continuation of Ser. No. 796,295, Jan. 22, 1969,

abandoned, which is a'continuation of Ser. No. 544,364, Apr. 22, l966, abandoned.

[52] US. Cl. ..23/209.l, 23/209.2, 264/29 [5i] Int. Cl. ..'......C0lb 31/04 [58] Field of Search ..23/209.1, 209.2; 264/29, 105;

l36/l2l, 122; 252/502; 260/649 [56] References Cited UNITED STATES PATENTS 2,500,209 3/1950 Sheaetal. ..264/l05 2,683,107 7/1954 Juel ..2e4/29x FOREIGN PATENTS OR APPLICATIONS 485,658 8/1952 Canada ..264/29 OTHER PUBLICATIONS Hubbard Kirk-Othmer Encyclopedia of Chemical Technology 2nd Ed., Vol. 5, 1965, pages 289- 297 Primary Examiner- Edward J. Meros Attorney-H. l-iume Mathews and Edmund W. Bopp [5 7] ABSTRACT 2 Claims, No Drawings of making the same. More particularly, the invention relates to carbonaceous articles such as graphite electrodes and graphite nipple stocks which have reduced coefficients of expan- 2 100 37 Aroclor 1242 5.0 11.9 3 100 37 Aroclor 1260 5.0 11.9 4 100 22 Aroclor 5460 22.0 50.0 5 1 00 39 None 0.0 0.0 6 100 40 None 0.0 0.0 7 100 41 None 0.0 0.0 8 100 37 Unchlorinated 5.0 11.9

biphenyl sion and increased flexural strengths, and methods of making The Aroclor compounds in the above table are chlorinated the same.

Shaped graphite articles are customarily made by mixing a crushed carbonaceous aggregate filler material comprised of such carbons as calcined petroleum coke, anthracite charcoal, electrode carbon scrap, metallurgical coke, lampbla'ck, natural graphite, or the like, with a sufficient amount of pitch to serve as a binder. This mixture is usually made above the melt- .ing point of the pitch to secure distribution of the pitch throughout the carbon aggregate. Small amounts of lubricant, such as black oil, may. be added shortly before the mixing is completed, especially where the articles involved are to be formed by extrusion molding. The mixture is cooled somewhat to congeal the binder, after which it is then compressed or extruded into the desired shape, then baked tocarbon ize the binder, after which the baked carbon body may be subjected to higher temperature to graphitize the carbon and the carbonized binder which holds it together.

Constant efforts are being made throughout the graphite industry to improve the-physicaland electrical properties of graphite articles. Thesubject matter of this invention resides in the discovery that the addition of relatively small amounts of chlorinated polyphenyls to the carbonaceous ingredientsof the article to be formed prior to the mixing of said ingredients results in the finished article, after graphitization, having'a substantially reduced coefficient of thermal expansion and increased flexural strength. This phenomena occurs even though substantially all, if not entirely all, of the chlorine in the chlorinated polyphenyl is give off during the baking and graphitizing of the carbonaceous article. I

It is accordingly an object of this invention to provide an im proved carbonaceous article of manufacture and a method of making the same.

It is another object of the invention to provide an improved graphite body having a low coefficient of thermal expansion and/or high flexural strength, and a method of making the same.

It is yet another object of this invention to provide an improved graphite electrode having a low coefficient of thermal expansion and/or high flexural strength, and a method of making the same. g

It is another object of the invention to provide a raw batch composition which when processed into a graphite bodyby conventional graphitizing techniques will form a finished graphite body having a low coefficient of thermal expansion and high flexural strength.

Other objects and advantages of the invention will become apparent as the description proceeds. I 7

As previously noted, graphite bodies formed from raw batch compositions which contain a chlorinated polyphenyl additive exhibit improved physical properties. The graphite bodies will of course be useful in many applications. As illustrative of the improved properties in such bodies, graphite electrodes of the type normally used as industrial furnace operations were prepared and tested. The electrodes tested were formed from the raw batch composition as set forth in Table l.

polyphenyls available commercially from Monsanto Chemical Company and are coded as to type. When the first two digits are 12, the material is. a biphenyl. When they are 54, the material is a terphenyL'The second set of digits indicates the weight percent of chlorine in the compounds.

In the manufacture of graphite electrodes, all raw materials are first weighed out and placed in a suitable mixer. The mixing is generally done at a temperature of 70 to 200 C, depending on the melting point of the pitch binder, and for a time of 20 to minutes. In the case of the mixes containing chlorinated polyphenyls, it is important that complete miscibility of the pitch and chlorinated polyphenyl is obtained.

Near the end of the mixing cycle, small amounts of lubricant maybe added, especially for extrusion molding of the mix. The mixture is then compressed or extruded into the desired shape, baked to a temperature of about 600 to l,000 C for a period of 5 to 60 days to carbonize the binder, and then fired to a temperature of 2,200 C or higher to graphitize the baked article. More specific details of graphite electrode manufacture are found in the Kirk-Othmer Encyclopedia of Chemical Technology, Vol.4, Second Edition, pages 158 to 200.

As a specific example of the manner in whichthe raw batch composition of this invention is converted into an improved graphite article, the composition identified as Example 1 in Table l was mixed in a sigma-blade mixer at a temperature of C for 60 min. The mixed compositionwas allowed to cool slightly to congeal the binder and then extruded into 5.5 in. diameter electrodes The electrodes were then baked at a temperature of 750 C for 20 days to carbonize the binder and then fired at a temperature of 2,750" C for 28 hours using conventional equipment and techniques, as described in the aforementioned Kirk-Othmer encyclopedia.

All of the examples in Table l were processed in a manner similar to that set forth for Example 1. The electrodes were tested and exhibited the proporties shown in Table I1.

TABLE II Average Sp. Res. CTE Example Density X 10 ohm-in. PS X l 0'/C. No. g./cc.) Long Trans. (p.s.i.) Trans.

Examples 5, 6, and 7 of Tables 1 and ll were made from compositions with a pitch binder and no additive. It can be seen that the transverse coefficient of thermal expansion (CTElwas in the range of about 4.1 to 4.2, and the flexural strength was in the range of 1,800 1,900 psi. By the addition of 12.2 percent chlorinated terphenyl based on the total weight of the binder, the CTE was reduced to 3.10 (a reduction of about 25 percent), and the flexural strength increased to 2,394 psi. It should be noted in Example 4, however, that when the chlorinated terphenyl reached 50 percent by weight of total binder, the CTE'has returned to approximately the same value as when pitch alone formed the binder. The test results illustrated in Table ll, and other data not reproduced here, have determined the beneficial range of chlorinated polyphenyls to be about 5 to 50 percent of the total weight of the binder.

It has also been established that best results are obtained when the chlorinated polyphenyls have relatively high concentrations of chlorine. For example, note that in Example 8 where the polyphenyl was unchlorinated, the transverse CTE approached the CTE of Examples 5, 6, and 7 which used the pitch binder, and the flexural strength was drastically reduced. It is preferred that the chlorine content be at least 50 percent of the total weight of the chlorinated polyphenyl, although lower amounts such as 40 percent chlorine will produce beneficial results.

Analysis of graphite electrodes made from compositions which contain chlorinated polyphenyls have established that most, if not all, of the chlorine present in the original compositions is lost during the baking and graphitizing process.

In addition to the improvement in the above-discussed physical properties, electrodes made in accordance with this invention exhibit higher coking values, coking values being defined as the ratio of the weight of coked pitch in the baked body to the weight of the pitch in the unbaked body.

Obviously many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to be understood that within the scope of the impending claims the invention may be practiced otherwise than as specifically described.

We claim:

I. A method'for producing a graphite article displaying a low coefficient of thermal expansion and high flexural strength, comprising in sequence the steps of: mixing a carbonaceous filler material and a binder of pitch together with about 12 percent by weight of said pitch of an additive selected from a chlorinated biphenyl and a chlorinated terphenyl, each having a chlorine content of at least 50 percent based on the total weight of said additive, to form a raw batch composition, said mixing step being for a time and at a temperature sufficient to secure complete miscibility of the pitch and chlorinated additive; thereafter forming said raw batch composition into an article of the desired size and shape; baking the formed article to carbonize the binder; and firing the thus baked article to form a finished graphite article.

2. A method in accordance with claim 1 wherein said mixing is conducted at a temperature of from about 70 to 200 C for a time duration of from about 20 to minutes. 

2. A method in accordance with claim 1 wherein said mixing is conducted at a temperature of from about 70* to 200* C for a time duration of from about 20 to 120 minutes. 